Abstract C032: Combination CAF/myeloid targeting in PDAC
Authors: Marie C. Hasselluhn, Lukas J. Vlahos, Dafydd Thomas, Alvaro Curiel Garcia, Amanda R. Decker, Tanner C. Dalton, Stephen A. Sastra, Carmine F. Palermo, Andrea Califano, Kenneth P. Olive
Journal: Cancer Research (2022)

Abstract Immunotherapy has revolutionized clinical care for many cancers, yet these treatments fail to control disease in many patients and new strategies are needed to improve anti-tumor immunity and enhance response rates. There is great need for an increased understanding of the cellular crosstalk within tumors and the identification of stromal and immune populations involved in shaping the tumor microenvironment (TME). Local immunosuppression (LIS) is one of the striking hallmarks of Pancreatic Ductal Adenocarcinoma (PDAC), a disease that is highly resistant to existing immunotherapies. Oncogenic Kras activation in tumor cells promotes the invasion and proliferation of tumor-supporting stromal cells, while excluding cancer-targeted cytotoxic T cells. LIS is mediated by multiple subtypes of cancer-associated fibroblasts (CAFs) and myeloid cells resident within the tumor parenchyma. Multiple prior attempts to reverse LIS in PDAC by targeting individual stromal cell populations have been unsuccessful, alluding to the complexity of stromal crosstalk within the TME. The stromal diversity of PDAC complicates investigating paracrine cascades involving multiple cell types. To decipher diverse drug effects on altering the TME, we employ in vivo studies in mouse models recapitulating the human disease, as well as a novel tumor explant model that enables the short-term culture of intact human or murine PDAC. Importantly, PDAC explants maintain their histopathological architecture and cellular diversity over time. This medium-throughput platform allows for testing of multiple drugs and mechanistic hypotheses in the native PDAC TME. We show in preliminary data that Smoothened inhibition (SMOi) decreases proliferation and activity of myCAFs, but provokes the expansion of CD11b-positive myeloid cells in vivo. Thus, we hypothesize that LIS in PDAC is maintained by a delicate balance between myCAFs and myeloid cells, preventing effective T cell invasion. Single cell RNA-seq data comparing ctrl vs. SMOi-treated murine PDAC elucidates stromal subpopulations involved in the LIS phenotype and guides the identification of myeloid subtypes emerging after SMOi. Strikingly, we demonstrated that simultaneous SMOi and targeting myeloid cells via anti-Gr1 or CCR1 inhibition (CCR1i) significantly elevates cytotoxic T cell numbers within the TME. We are currently investigating whether the activity of these T cells may be further potentiated through combination with immunomodulatory agents. By testing various treatment combination in the same TME, we will identify the best synergistic effects for future immunotherapy approaches in human PDAC. In summary, we are elucidating the complex mechanism behind LIS in PDAC by employing our novel explant culture system alongside in vivo studies. We aim to develop a translatable regimen to neutralize LIS, reactivating the cytotoxic T cells in the tumor periphery to invade, proliferate, and attack cancer cells. Citation Format: Marie C. Hasselluhn, Lukas J. Vlahos, Dafydd Thomas, Alvaro Curiel Garcia, Amanda R. Decker, Tanner C. Dalton, Stephen A. Sastra, Carmine F. Palermo, Andrea Califano, Kenneth P. Olive. Combination CAF/myeloid targeting in PDAC [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C032.